How do you define what is alive and what is not alive? Why is a planet full of life is different from a planet without life? I think that the answers are about order and chaos, and life sides with order.
Life is fundamentally a system of information organisation and storage. A living person is a closed system of information storage and utilisation, used to bring order to a disordered system. To die is to terminally lose information cohesion, liberating this to the next shell domain of information, for example, civilisation, which itself is more ordered than nature, which we could define as a life bearing but human-free domain, which is more ordered than lifeless nature, such as a planet without life.
The key definition of life is an information storage and processing entity with the ability to increase the order of a disordered system.
This definition of life and death has several implications.
On the surface, it removes the contemporary definitions of the need to metabolise or replicate, but on further analysis, this can still apply: for example a filing cabinet can store information but does not order its surroundings, and so could not be considered alive. Reproduction could be seen as an extension of the utility to order the universe, and is thus compatible with this definition. Taking in food helps maintain the informational integrity of the body vs. not taking food.
Plants and bacteria store and pass on information, and can order their environment, but humans can order a system more effectively.
Machines which can self-order the world should be considered alive. At time of writing, machines are usually tools for humans, but computers can self-order small pockets of information: for example ordering computer files. Small robots could order cubes upon a table, or mow a lawn. A ruler, as a converse example, cannot; despite aiding humans to order things, making a ruler a tool rather than alive.
We have varying control over what we are capable of ordering, and this defines how alive we are. Humans can almost control all things, as a species, and almost all humans have some influence over the rest of the species. It is perhaps this that makes humans the paragon of living things.
